S Poetry

S Poetry starts with the basics of the S language (of which R is a dialect). It then goes on to more advanced issues, including good programming techniques. Many of the deficiencies that are pointed out have now been fixed in R and S+.
The parts that are most helpful include the glossary and the chapter on higher dimensional arrays. The 'genopt' function (which is R-compliant and available on the Burns Statistics website) -- though not particularly a nice example of programming -- is one of the most useful functions.